Since the 1970s, the IAEA has been involved in the analysis of fuel failures in water cooled reactors in normal (nonaccident) operational conditions. This updated version of IAEA Nuclear Energy Series No. NFT2.1 provides information on all aspects of fuel failures in current nuclear power plant operations. It summarizes fuel failure occurrences and their mechanisms and root causes, as well as fuel failure prevention and management in plant operation for 97% of light and heavy water cooled nuclear power units operated worldwide during the period 2006-2015. Data on fuel failures from 1987 to 2006 extracted from three previous IAEA fuel failure reports are included and analysed in the present publication, together with the 2006-2015 fuel failure data, to reveal long term tendencies in fuel performance. In addition to fuel rod leakers, fuel structural damages and other fuel assembly issues are considered in the report.